Crying out when we get hurt is a natural and unstoppable instinct.
Now scientists think they have found the reason for our yelps - it helps us withstand the pain.
The effort of shouting the word 'ow' interferes with pain messages travelling to the brain, a new study suggests.
But the new research indicates that we may actually do so to distract ourselves from the feeling of pain.
The scientists, whose study is published in the Journal of Pain, say that expressions of pain are shared across language barriers.
'Ow' or 'ouch' are shouted in English, South Africans yell 'eina', Italians say 'ahia' and Chinese 'aiyo'.
The researchers, from the departments of psychology and neurobiology at the National University of Singapore, wrote: 'Shared among these is a sound during which the mouth simply opens, the tongue lies flat and the lips remain unrounded.
'It is a simple sound that requires little articulatory control, while maximizing volume output.
'As such it may be used quite easily and effectively when in pain.'
The scientists tested for how long volunteers could keep their hands in painfully cold water.
The 56 participants were allowed to shout 'ow' when they felt pain, and then the experiment was repeated four more times with the volunteers asked to stay silent.
In one test they could press a button when they felt pain, in another they were played a recording of themselves shouting 'ow', in another the recording was of another person shouting 'ow', and in the fifth they just sat passively until they could no longer withstand the pain.
The results showed that the participants were able to stand the pain for longest when they were allowed to shout out.
They managed nearly 30 seconds on average, five seconds more than when they were told to sit and do nothing.
Hearing recordings of a yelp did nothing to increase the time they could withstand the pain, suggesting that 'vocalising in pain is not only communicative,' the researchers said.
They wrote: 'We observed higher pain tolerance when participants said "ow" than when they did nothing.
'We have demonstrated that vocalizing in and of itself is potentially analgesic. We found that a simple vocal act such as saying "ow" helps individuals cope with pain.'
Exactly how the process works is not clear, but they think the automatic messages travelling to the vocal part of the brain interfere with the pain messages.
'One may explain the present results in the context of sensorimotor processes,' they write.
'Motor acts engage both parts of the peripheral nervous system. Muscular changes feedback to the brain may thus compete with pain related processes.'
<<Print>>